Shared centiMorgan (cM) Calculator
Enter the amount of DNA you share with a match to calculate the possible relationships. This tool uses standard probability distributions and works entirely in your browser—no data is logged or sent to any server.
Understanding the CentiMorgan (cM)
A centiMorgan is a unit of genetic linkage. It is not a physical distance, but a measure of probability that a section of DNA will be passed on intact to the next generation.
When two people take an autosomal DNA test, the company compares their chromosomes. If they find identical segments of DNA on the same chromosome in both people, they add up the length of those segments in centiMorgans. The higher the number, the closer the relationship.
Manual Lookup Table (Averages)
| Relationship | Average cM | Expected Range |
|---|---|---|
| Parent / Child | 3,400 | 3,300 - 3,490 |
| Full Sibling | 2,613 | 2,200 - 3,300 |
| Grandparent / Grandchild | 1,754 | 1,300 - 2,300 |
| First Cousin | 866 | 400 - 1,300 |
Source: The Shared cM Project (Blaine Bettinger). Averages represent autosomal DNA shared across populations without significant pedigree collapse.